Exhaust gas heat exchanger

ABSTRACT

An exhaust gas heat exchanger for an internal combustion engine includes an exhaust passage and an offset fin. The offset fin includes a plurality of side walls and a plurality of top walls. The offset fin is defined into a plurality of segments that are offset from each other in an offset direction. One of the plurality of top walls of the offset fin has a projection that inwardly projects therefrom. The projection is provided to one of the plurality of segments. The projection of the one of the plurality of segments is opposed to an upstream end portion of the other one of the plurality of side walls of the other one of the plurality of segments that is positioned adjacently downstream of the one of the plurality of segments in the circulation direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-268996 filed on Oct. 17, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas heat exchanger that exchanges heat between (a) cooling fluid and (b) exhaust gas discharged from an internal combustion engine.

2. Description of Related Art

A conventional exhaust gas heat exchanger is described in, for example, JP-A-2003-106785 (corresponding to EP1411315A1). For example, the exhaust gas heat exchanger of JP-A-2003-106785 has offset-type inner fins that are offset arranged in an exhaust passage within a tube, through which exhaust gas flows. A projection inwardly projects from a top wall of the inner fin, and exhaust gas flows through the exhaust passage in a meandering path (zigzag path) toward opposing top wall.

More specifically, the inner fin includes segments that are offset from each other. For example, the segments are arranged in a flow direction of exhaust gas and are alternately displaced from each other in a direction perpendicular to the flow direction. The projection inwardly projects from the top wall of each of the segments and serves as a triangular wing. Furthermore, each segment includes two wings that are arranged in the exhaust gas flow direction.

In the above exhaust gas heat exchanger, the projections (wings) cause exhaust gas to flow in a zigzag manner, and exhaust gas is caused to generally uniformly collide with each projection in the exhaust passage. Thus, the flow of exhaust gas is effectively disturbed such that a heat transmission rate is effectively improved. Also, by disturbing the flow of exhaust gas, a flow velocity of exhaust gas is increased, and thereby it is possible to blow off unburned substances (PM) in exhaust gas that are attached to a wall surface of the inner fin. As a result, the accumulation (deposition) of the unburned substances on the wall surface is limited.

However, because the exhaust gas heat exchanger of JP-A-2003-106785 has multiple projections (for example, two projections) at each segment, each segment has a large dimension in an exhaust gas flow direction. As a result, a leading edge effect of the segment is not sufficiently achieved. In other words, the increase of the dimension of the segment in the exhaust gas flow direction thickens a boundary layer, which is formed at a side wall of the segment, and which extends in a downstream direction from the leading edge of the segment. Thus, there may be generated a region at downstream part of the segment, in which the flow velocity of exhaust gas is reduced compared with an upstream part of the segment. Thus, a heat transmission rate in a heat exchange between exhaust gas and cooling fluid may deteriorate disadvantageously. Furthermore, the increase of the region, in which exhaust gas flows slowly, decreases a surface shear force that would blows off unburned substances. As a result, the decreased surface shear force may enhance the accumulation of unburned substances on the side wall disadvantageously.

Also, as shown in FIG. 8, a stagnation region RA, within which exhaust gas tends to be stagnant, is more likely to be formed between multiple projections 1240 (for example, two projections 1240) of a segment 1230. Thus, the decrease in flow velocity of exhaust gas may be caused. Accordingly, the decrease in flow velocity of exhaust gas may degrade the heat transmission rate. Also, the decrease in flow velocity of exhaust gas may degrade the surface shear force that would otherwise blow off the unburned substances. As a result, the accumulation of the unburned substances on the wall surface may be enhanced disadvantageously.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.

To achieve the objective of the present invention, there is provided an exhaust gas heat exchanger for an internal combustion engine, the exhaust gas heat exchanger including an exhaust passage and an offset fin. Exhaust gas discharged from the internal combustion engine flows through the exhaust passage. The offset fin is provided within the exhaust passage. The offset fin has a cross sectional shape of a rectangular waveform taken along a plane perpendicular to a circulation direction of exhaust gas. The offset fin includes a plurality of side walls, which forms leading and trailing parts of the waveform, and a plurality of top walls, which forms crest and valley parts of the waveform. The offset fin is defined into a plurality of segments that are offset from each other in an offset direction, in which the plurality of side walls are arranged in series. Heat is exchanged between (a) exhaust gas flowing through the exhaust passage and (b) cooling fluid flowing at an exterior of the exhaust passage. One of the plurality of top walls of the offset fin has a projection that inwardly projects therefrom. The projection is provided to one of the plurality of segments. The projection of the one of the plurality of segments is opposed to an upstream end portion of the other one of the plurality of side walls of the other one of the plurality of segments that is positioned adjacently downstream of the one of the plurality of segments in the circulation direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating an EGR (exhaust gas recirculation) system having an EGR gas cooler according to a first embodiment of the present invention;

FIG. 2 is a front view illustrating the EGR gas cooler;

FIG. 3 is a perspective view illustrating a tube;

FIG. 4 is a perspective view illustrating an inner fin;

FIG. 5 is a perspective view schematically illustrating a flow of EGR gas at the inner fin;

FIG. 6 is a plan view of the inner fin viewed in a direction of VI of FIG. 5 for schematically illustrating a flow of EGR gas at the inner fin;

FIG. 7A is a diagram illustrating a distribution of a surface shear force of EGR gas on the side wall in the inner fin viewed in a direction of VIIA of FIG. 7B;

FIG. 7B is another plan view of the inner fin viewed in the direction of VI of FIG. 5; and

FIG. 8 is a plan view schematically illustrating a flow of EGR gas of a conventional art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

In the first embodiment, an exhaust gas heat exchanger of the present invention is applied to an EGR gas cooler 100 for a diesel engine 10. FIG. 1 is a schematic diagram illustrating an EGR (exhaust gas recirculation) system having the EGR gas cooler 100 according to the present embodiment.

The EGR functions to reduce nitrogen oxides in exhaust gas of the engine 10 (internal combustion engine) for a vehicle, and includes an exhaust gas recirculation pipe 11, an EGR valve 12, and the EGR gas cooler 100. The exhaust gas recirculation pipe 11 causes a part of exhaust gas discharged from the engine 10 to flow back to upstream of (or intake side of) the engine 10.

The EGR valve 12 is provided in the exhaust gas recirculation pipe 11, and adjusts an amount of exhaust gas (hereinafter, referred as EGR gas), which flows through the exhaust gas recirculation pipe 11, in accordance with an operation of the engine 10. The EGR gas cooler 100 is a heat exchanger that exchanges heat between EGR gas and coolant for the engine 10 in order to cool EGR gas, and is provided between the EGR valve 12 and an exhaust port of the engine 10.

A structure of the EGR gas cooler 100 will be described with reference to FIGS. 2 to 4. FIG. 2 is a front view illustrating the EGR gas cooler 100, FIG. 3 is a perspective view illustrating an appearance of a tube 110, and FIG. 4 is a perspective view illustrating an appearance of an inner fin 120.

The EGR gas cooler 100 includes, as shown in FIG. 2, the tube 110, the inner fin 120, a casing 130, core plates 140, collectors 150, 160, an inlet port 170, and an outlet port 180. The above components are made of, for example, a stainless material that has great heat resistance and corrosion resistance, and the components are joined respectively by blazing.

As shown in FIG. 3, the tube 110 is a pipe member that defines therein an exhaust passage 111, through which EGR gas flows. The tube 110 has a flat rectangular cross sectional shape taken along a plane perpendicular to a circulation direction of EGR gas. The tube 110 includes two tube plates 110A, 110B, and each of the tube plates 110A, 110B is press molded into a shape such that each tube plate has a cross section having a shallow U-shape, for example. Opening end portions of the U-shaped tube plates 110A, 110B are joined to each other to form the tube 110. Multiple tubes 110 are stacked onto one another in a stack direction. Opposing surfaces of the tubes 110, which surfaces correspond to long sides of the flat cross section, face each other in the stack direction.

The opposing surface of the tube 110 is provided with protrusions 112, 113 that outwardly projects from the opposing surface. The protrusions 112, 113 are formed simultaneously when each of the tube plates 110A, 110B is press molded.

The protrusion 112 is provided at a position on an inlet-side of the tube 110 in a longitudinal direction and is provided downstream of the inlet port 170 for coolant. The protrusion 112 extends along the opposing surface of the tube 110 in a lateral direction perpendicular to the circulation direction of EGR gas, and each of the longitudinal direction end portions of the protrusion 112 is located at a position that is away, by a predetermined distance, from a plane of the short side of the flat cross section of the tube 110. The protrusion 112 defines a relatively small space around the inlet port 170, through which coolant flows into the casing 130, such that the flow velocity of coolant is increased at a position near the inlet of the casing 130 for EGR gas.

Also, each of a pair of the protrusions 113 is separated from each other in the lateral direction as shown in FIG. 3, and multiple pairs of the protrusions 113 are arranged downstream of the protrusion 112 and are aligned in the circulation direction of EGR gas (FIG. 2) by predetermined intervals. The protrusion 113 has an oval shape, for example, and projects from the opposing surface of the tube 110. In the stacked tubes 110, the crests of the protrusions 112 contact each other, and the crests of the protrusions 113 contact each other (FIG. 2) such that dimensions of clearances defined between the multiple tubes 110 are appropriately kept.

An inner fin 120 serves as a heat transmission member that exchanges heat between EGR gas and coolant, and is provided within the tube 110 or within the exhaust passage 111. The inner fin 120 has a cross section, which has a rectangular waveform, taken along a plane perpendicular to the circulation direction of EGR gas as shown in FIG. 4. More specifically, side walls 121 and top walls 122 define the rectangular waveform as shown in FIG. 4. The side wall 121 corresponds to leading and trailing parts of the waveform of the inner fin 120, and connects inner surfaces of the opposing tube plates 110A, 1108 of the tube 110. Also, the top walls 122 correspond to crest and valley parts of the waveform of the inner fin 120, and contact and are joined to the inner surface of the opposing surface (tube plate) of the tube 110.

The inner fin 120 is an offset-type inner fin that is defined into multiple segments 123 arranged in a crest direction, in which the crests (top walls) of the fin 120 extend. Also, the multiple segments 123 are offset from each other in an offset direction, in which the side walls 121 are arranged in series to form the waveform. More specifically, one segment 123 is offset or displaced from the other segment 123 by an offset amount that is generally equivalent to a half of a width dimension of the waveform. The width dimension is measured between the adjacent side walls 121, or is measured between the leading part and the trailing part of the waveform. The above offset segments 123 are arranged in the circulation direction of EGR gas and are alternately offset from each other. Also, the width dimension of the waveform of the segment 123 and the dimension of the segment 123 measured in the circulation direction of EGR gas are determined to be a minimum dimension such that a projection 124, which will be described later, is formed on the top wall 122.

The top wall 122 has a projection 124 that inwardly projects from the top wall 122. The projection 124 is provided for each of the segments 123. The multiple segments 123 are adjacently arranged in the circulation direction of EGR gas, and, for example, a first segment 123 of the multiple segments 123 is located upstream of a second segment 123 of the multiple segments 123 in the circulation direction. In the above arrangement, the projection 124 of the first segment 123 is located to be oppose to an upstream end portion 121a of the side wall 121 of the second segment 123 (see FIGS. 5 and 6). As shown in FIG. 6, the upstream end portion 121 a of the side wall 121 is an upstream part of the side wall 121.

Furthermore, the projection 124 serves as a raised part 124 that is made by cutting the part of the top wall 122, and by raising the cut part from the top wall 122 such that the raised part 124 inwardly project from the top wall 122. The raised part 124 has a triangular shape, and in the present embodiment, the raised part 124 is referred as a wing 124. The wing 124 is raised or folded along a folding side 124 a as shown in FIG. 4. The wing 124 is positioned such that the folding side 124 a is angled relative to the circulation direction of EGR gas. Also, an amount, by which the wing 124 of the second segment 123 projects from the top wall 122, is designed to be larger than an amount, by which the wind 124 of the first segment 123 that is located upstream of the first segment 123 in the circulation direction of EGR gas. In other words, the wings 124 are designed such that the projection amounts of the wings 124 become greater toward the downstream side of the inner fin 120. Also, the folding side 124 a of each of the segments 123, which are arranged in the circulation direction of EGR gas, is alternately angled relative to the circulation direction as shown in FIG. 6. More specifically, if one segment 123 is angled toward the one side relative to the circulation direction, the other segment 123 that is located immediately downstream of the one segment 123 is angled toward the other side opposite from the one side relative to the circulation direction.

Also, as shown in FIG. 6, a dimension of the segment 123 measured in the circulation direction of EGR gas is defined as L1 (hereinafter referred as a segment dimension L1), and a dimension of the wing 124 measured in the circulation direction of EGR gas is defined as L2 (hereinafter referred as a wing dimension L2). In other words, the wing dimension L2 corresponds to a dimension of the projection in the exhaust gas circulation direction. The segment dimension L1 is equal to or greater than the wing dimension L2. Also, the segment dimension L1 is equal to or less than a dimension (7×L2) that is seven times longer than the wing dimension L2. For example, an equation of L2≦L1≦7×L2 is satisfied. More specifically, the segment dimension L1 may be equal to or less than a dimension (4×L2) that is four times longer than the wing dimension L2. Thus, another equation of L2≦L1≦4×L2 may be satisfied. The above description of “the segment dimension L1 is equal to or greater than the wing dimension L2” indicates that the segment dimension L1 is required to be at least equivalent to the wing dimension L2 in order to physically substantially form the wing 124 on the segment 123.

As shown in FIG. 2, the casing 130 is a rectangular tubular container that receives therein the tubes 110, which are stacked onto one another, and which are joined through the respective protrusions 112 and the respective protrusions 113. Also, the casing 130 defines therein coolant passages 131, through which coolant flows around the stack of the tubes 110. The coolant passages 131 are defined between the tubes 110, and between the tubes 110 and the casing 130 as shown in FIG. 2.

The core plate 140 is a plate member that has a shallow bowl shape. A bottom surface of the core plate 140 is provided with multiple tube holes. A pair of the core plates 140 is provided at the longitudinal ends of the tubes 110, and the tube hole of each core plate 140 receives therein the respective longitudinal end portion of the tube 110 in a fixed manner. Thus, the multiple tubes 110 are supported by the pair of the core plates 140. The pair of the core plates 140 are joined to inner peripheral surfaces of longitudinal opening ends of the casing 130. The pair of the core plates 140 defines the coolant passage 131 within the casing 130 and defines internal spaces of the collectors 150, 160.

The inlet-side collector 150 has a funnel shape for distributing EGR gas to each of the tubes 110, and an end of the inlet-side collector 150 having a wide opening area is joined to a longitudinal end opening of the casing 130. More specifically, as shown in FIG. 2, the right end of the inlet-side collector 150 is joined to the left end of the casing 130. For example, the right end of the inlet-side collector 150 is joined to the inner peripheral surface of the opening of the respective core plate 140 that is joined to the casing 130. The other end of the inlet-side collector 150 having a smaller opening area is joined to a joint member 151 that is connected to the exhaust gas recirculation pipe 11.

The outlet-side collector 160 has a funnel shape and collects EGR gas that flows out of each tube 110. An end of the outlet-side collector 160 having a wide opening area is joined to the other longitudinal end opening of the casing 130. More specifically, in FIG. 2, the left end of the outlet-side collector 160 is joined to the right end of the casing 130. For example, the left end of the outlet-side collector 160 is joined to the inner peripheral surface of the opening of the respective core plate 140. The other end of the outlet-side collector 160 having a smaller opening area is joined to a joint member 161 that is connected to the exhaust gas recirculation pipe 11.

The inlet port 170 is a pipe member that introduces coolant into the coolant passage 131, and is joined to the casing 130 at a position on an inlet side of the casing 130 for EGR gas such that the interior of the inlet port 170 is communicated with the interior (the coolant passage 131) of the casing 130. The inlet port 170 longitudinally extends in a direction that is parallel to a plane of the opposing surface of the tube 110.

The outlet port 180 is a pipe member, through which coolant in the coolant passage 131 is discharged from the casing 130. The outlet port 180 is joined to the casing 130 at a position on an outlet side of the casing 130 for EGR gas such that the interior of the outlet port 180 is communicated with the interior (the coolant passage 131) of the casing 130. The outlet port 180 longitudinally extends in a direction that is orthogonal to a plane of the opposing surface of the tube 110.

The operation and advantages of the above EGR gas cooler 100 will be described with reference to FIGS. 5 and 6. FIGS. 5 and 6 are diagrams for schematically illustrating flow of EGR gas at the inner fin 120.

In the EGR gas cooler 100 of the present embodiment, when the EGR valve 12 is opened, EGR gas, which is a part of exhaust gas, flows into the EGR gas cooler 100 through the inlet-side collector 150. Then, EGR gas is distributed to each the tube 110, and flows through the exhaust passage 111 of each of the tubes 110. Then, EGR gas that has passed through the exhaust passage 111 is collected at the outlet-side collector 160, and then is supplied to the inlet side of the engine 10 through the EGR valve 12.

Coolant of the engine 10 flows into the casing 130 through the inlet port 170, and then the coolant that has passed through the coolant passages 131 is discharged from the casing 130 through the outlet port 180. Thus, coolant returns to the engine 10.

In the above, heat is exchanged between (a) EGR gas that flows through the exhaust passage 111 and (b) coolant that flows through the coolant passages 131, and as a result EGR gas is cooled. Because thus cooled EGR gas is supplied to the pipe upstream of the engine 10, a maximum temperature for combustion of the engine 10 is effectively reduced. As a result, the generation of an amount of nitrogen oxides in the combustion is suppressed.

FIG. 5, as shown in FIG. 6, EGR gas that flows through the exhaust passage 111 generates vortex when EGR gas passes by the wing 124 (projection) of the inner fin 120. More specifically, vortex is generated around the wing 124 such that flow of vortex goes around toward a back side (downstream side) of the wing 124. As a result, EGR gas is caused to flow in a direction, in which the wing 124 is inclined or angled relative to the longitudinal direction of the exhaust passage 111, because of the go-around force of the vortex when EGR gas passes by the wing 124.

When EGR gas passes by the wing 124 of one segment 123, EGR gas collides with the upstream end portion 121 a of the other segment 123, which is located adjacently downstream of the one segment 123. As a result of the collision, turbulent is generated to the flow of EGR gas. Thus, EGR gas with turbulent passes by the downstream wing 124.

In the present embodiment, the segments 123 of the inner fin 120 are arranged in the circulation direction of EGR gas in a zigzag manner. For example, the segments 123 are regularly and alternately displaced (or offset) from each other in an offset direction orthogonal to the circulation direction. Also, because the inclined direction of the folding side 124 a of the wing 124 of each segment 123 is alternately changed, the flow direction of EGR gas is changed at each wing 124. As a result, EGR gas flows meanderingly (in a zigzag manner) through the exhaust passage 111 that extends in the circulation direction. Note that, because the wings 124 of the inner fin 120 are formed at the upper and lower top walls 122 as shown in FIG. 4, the wing 124 also causes EGR gas to flow in a direction from one top wall 122 to the other top wall 122 that is opposed to the one top wall 122. For example, the wing 124 located at the lower top wall 122 causes the EGR gas to flow toward the upper top wall 122 that is opposed to the lower top wall 122.

In the present embodiment, where EGR gas is caused to flow as above, one segment 123 of the inner fin 120 is provided with one projection (wing 124). As a result, it is possible to effectively reduce the dimension (the segment dimension L1) of the one segment 123 measured in the circulation direction of EGR gas compared with the conventional art. Accordingly, a leading edge effect caused by the upstream end portion 121 a of the segment 123 is sufficiently achieved. In other words, because it is possible to minimize the dimension of the one segment 123 measured in the EGR gas flow direction, it is possible to make a boundary layer thinner, which is formed at the side wall 121 of the one segment 123 in a range from the upstream end portion 121 a of the one segment 123 in a downstream direction of the flow. As a result, deterioration of a flow velocity of EGR gas at the downstream side is effectively limited, and thereby the heat transmission rate during the heat exchange between EGR gas and coolant is effectively improved. Furthermore, because it is possible to limit the deterioration of the flow velocity of EGR gas, it is possible to maintain a sufficient surface shear force required to blow off the unburned substances. As a result, the accumulation of unburned substances on the side wall 121 is effectively limited.

More specifically, the limitation of the accumulation of unburned substances on the side wall 121 will be detailed with reference to FIGS. 7A and 7B. FIG. 7A is a diagram illustrating a distribution of a surface shear force of EGR gas on the side wall 121A in the inner fin 120 viewed in a direction of VIIA of FIG. 7B, and FIG. 7B is a plan view of the inner fin 120 viewed in the direction of VI of FIG. 5. As shown in FIG. 7B, a pair of side walls includes a side wall 121A and a side wall 121B. FIG. 7A shows the distribution of the surface shear force caused by EGR gas on the side wall 121A viewed in a direction (upward in FIG. 7B) from the opposing side wall 121B. Because the flow of EGR gas collides with the upstream end portion 121 a of each segment 123, the turbulent is generated to the flow of EGR gas, and thereby the surface shear force of EGR gas at the upstream end portion 121 a is greater than the other part of the side wall 121A as shown in FIG. 7A. Because of the flow characteristic of EGR gas (the zigzag flow as shown in FIG. 7B), and also because of the leading edge effect of the side wall 121, the generation of stagnation regions in the flow of exhaust gas is limited as shown in FIG. 7A compared with the conventional art shown in FIG. 8. As a result, the heat transmission performance is further improved for limiting the accumulation ACC of unburned substances. For example, the stagnation region in the flow of exhaust gas corresponds to a region around the side wall 121A having a relatively lower surface shear force.

Also, because the projection (the wing 124) causes a vortex flow (turbulent flow) to exhaust gas, turbulent flow is generated to exhaust gas. As a result, the heat transmission rate is further improved. Furthermore, because the formation of the turbulent flow due to the projection (the wing 124) effectively increases the flow velocity of EGR gas, the surface shear force for blowing off the unburned substances is effectively enhanced. As a result, the accumulation of the unburned substances at the side wall 121 is further limited.

Because there is only one projection (the wing 124) formed on each segment 123, decrease in flow velocity of EGR gas between multiple projections (the wings) of the conventional segment described in the conventional art of FIG. 8 will not occur in the present embodiment. Thus, the deterioration of the heat transmission rate caused by the decrease in flow velocity of EGR gas is effectively prevented. Furthermore, because the decrease in flow velocity of EGR gas is effectively prevented, it is possible to maintain the sufficient surface shear force required for blowing off the unburned substances, and thereby the accumulation of the unburned substances on the wall of the inner fin 120 is effectively limited.

In general, the present embodiment effectively improves the leading edge effect of the offset-type inner fin 120 in order to limit the generation of the stagnation region in the flow of EGR gas. Thus, it is possible to further improve the heat transmission performance and also to limit the accumulation of the unburned substances.

Also, in the present embodiment, the projection of the inner fin 120 is made by cutting the top wall 122 and by raising the cut part in order to form the wing 124. As a result, the inner fin 120 is integral with the wing 124, and thereby the manufacturing cost is effectively reduced.

Also, in the present embodiment, the multiple segments 123 are meanderingly arranged in the circulation direction of EGR gas in a zigzag manner. Also, the wing 124 has the triangular shape, and the folding side 124 a of the wing 124 is angled relative to the circulation direction of EGR gas. Further, the projection amount, by which the wing 124 projects from the top wall 122, becomes larger toward the downstream side in the circulation direction of EGR gas. Furthermore, the inclined directions of the folding sides 124 a relative to the circulation direction of EGR gas are alternately changed as a function of the position of the folding side 124 a in the circulation direction.

Thus, it is possible to effectively form the vortex flow at a position downstream of the wing 124. Furthermore, exhaust gas meanderingly flows in the offset direction within the exhaust passage 111, and also exhaust gas flows in the direction from the lower top wall 122 to the upper top wall 122 or from the upper top wall 122 to the lower top wall 122. As a result, the heat transmission rate is further improved.

Also, in the design of the dimensions of the segment 123 and the projection 124 (wing), the segment dimension L1 (first dimension) is equal to or greater than the wing dimension L2 (second dimension), and the segment dimension L1 is equal to or less than a dimension that is seven times greater than the wing dimension L2. Due to the above design, the wing 124 effectively generates the vortex (turbulent flow) and effectively increases the flow velocity of EGR gas (or the surface shear force). As a result, it is possible to reliably limit the accumulation of the unburned substances at the side wall 121.

Other Embodiment

In the first embodiment, the wing 124 is the projection that is made by cutting the part of the top wall 122 of the inner fin 120 and by inwardly raising (bending) the cut part along the folding side 124 a. However, the wing 124 may be alternatively, for example, a projection, that is made by press work to project from the top wall 122. Also, alternatively, a projection may be made as a separate component and the separate projection may be fixed to the top wall 122.

Also, the projection is not limited to have the triangular shape of the wing 124. However, the projection may have a rectangular shape or a semicircular shape. Furthermore, the wing 124 is located to be angled relative to the circulation direction of EGR gas in the above embodiment. Alternatively, the wing 124 may be located to be perpendicular to the circulation direction of EGR gas.

Also, the inner fin 120 has the multiple segments 123, which are arranged in the circulation direction of EGR gas, and which are alternately offset from each other in the offset direction. However, the multiple segments 123 may be offset from each other in one direction.

Also, the EGR gas cooler 100 includes the coolant passages 131 that are defined between the tubes 110. More specifically, the core plates 140 receives and fixes the respective end portions of the multiple tubes 110, and the coolant passages 131 are defined between the tubes 110 within the casing 130 and the core plates 140. However, the EGR gas cooler 100 is not limited to the above configuration. For example, a swelling part may be formed to project outwardly from an outer periphery of each opposing surface of the tube 110, and the opposing swelling parts are joined to each other in a state, where the tubes 110 are stacked onto one another. As a result, a space is defined within the swelling parts, and the defined space may serve as an alternative coolant passage 131. In the above alternative case may be applied to an EGR gas cooler that does not have the core plates 140.

Also, in the above embodiment, the EGR (exhaust gas recirculation) system is applied to the diesel engine. However, the EGR may be alternatively applied to a gasoline engine.

Also, in the above embodiment, cooling fluid for the EGR gas cooler 100 employs coolant of the engine 10. However, cooling fluid for the EGR gas cooler 100 may alternatively employ the other coolant dedicated for a coolant circuit independent from the engine 10. The alternative coolant circuit may include, for example, a sub-radiator and a dedicated pump.

Also, in the above embodiment, the exhaust gas heat exchanger is applied to the EGR gas cooler 100 that cools EGR gas by using coolant. However, the exhaust gas heat exchanger may alternatively be applied to a heat recovery apparatus, which exchanges heat between (a) exhaust gas and (b) a certain target to be heated, such that the certain target is heated by exhaust heat. The certain target to be heated may be engine coolant at a time immediately after starting of a vehicle, engine oil, or an automatic transmission fluid.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. An exhaust gas heat exchanger for an internal combustion engine comprising: an exhaust passage, though which exhaust gas discharged from the internal combustion engine flows; and an offset fin that is provided within the exhaust passage, wherein the offset fin has a cross sectional shape of a rectangular waveform taken along a plane perpendicular to a circulation direction of exhaust gas, wherein the offset fin includes a plurality of side walls, which forms leading and trailing parts of the waveform, and a plurality of top walls, which forms crest and valley parts of the waveform, wherein the offset fin is defined into a plurality of segments that are offset from each other in an offset direction, in which the plurality of side walls are arranged in series, wherein: heat is exchanged between (a) exhaust gas flowing through the exhaust passage and (b) cooling fluid flowing at an exterior of the exhaust passage; one of the plurality of top walls of the offset fin has a projection that inwardly projects therefrom; the projection is provided to one of the plurality of segments; and the projection of the one of the plurality of segments is opposed to an upstream end portion of the other one of the plurality of side walls of the other one of the plurality of segments that is positioned adjacently downstream of the one of the plurality of segments in the circulation direction.
 2. The exhaust gas heat exchanger according to claim 1, wherein: the projection is made by cutting a part of the one of the plurality of top walls and by folding the cut part such that the projection projects inwardly from the one of the plurality of top walls.
 3. The exhaust gas heat exchanger according to claim 2, wherein: the plurality of segments is arranged in the circulation direction of the exhaust gas and is alternately offset from each other; the projection has a triangular shape and has a folding side, along which the projection is folded relative to the one of the plurality of top walls; the projection is provided such that the folding side is angled relative to the circulation direction of the exhaust gas; the projection is one of a plurality of projections, each of which projects from a corresponding one of the plurality of top walls; the projection, which projects from the one of the plurality of top walls, is a first projection; a second projection of the plurality of projections projects from the other one of the plurality of top walls that is positioned downstream of the one of the plurality of top walls in the circulation direction; a projection amount, by which the first projection projects from the one of the plurality of top walls, is smaller than a projection amount, by which the second projection projects from the other one of the plurality of top walls; and the folding sides of the plurality of projections are arranged in the circulation direction and are alternately angled relative to the circulation direction.
 4. The exhaust gas heat exchanger according to claim 1, wherein: exhaust gas is supplied to an inlet side of the internal combustion engine and is used for exhaust gas recirculation; and cooling fluid is a coolant that cools the internal combustion engine.
 5. The exhaust gas heat exchanger according to claim 1, wherein: each of the plurality of segments has a first dimension measured in the circulation direction of exhaust gas; the projection of the one of the plurality of segments has a second dimension measured in the circulation direction; and the first dimension is equal to or greater than the second dimension; and the first dimension is equal to or less than a dimension that is seven times larger than the second dimension. 